A turbomachine impeller is comprised of a disk and movable vanes rotatably driven by the disk under the effect of a fluid flow from upstream to downstream through the turbomachine. It is noted that the terms “upstream” and “downstream” are to be considered with respect to a general flow direction of fluids through the turbomachine, from upstream to downstream.
FIG. 1 shows a first turbine vane 10 generally extending along a longitudinal axis X, and conventionally including a blade 11 the bent profile of which is adapted to the aerodynamic functions it should fulfil in operation. At both its side ends, the blade 11 includes a leading edge 12 and a trailing edge 13, between which extend an active surface wall 14 and a passive surface wall. In FIG. 1, only the active surface side of the first vane 10 is visible. The first vane 10 also includes a shank 15 projecting from the blade 11 along the longitudinal axis X, and extending between the leading edge 12 and the trailing edge 13.
For mounting vanes, the disk includes on its periphery a plurality of evenly distributed teeth, radially outwardly projecting from the disk and extending between both side faces of the disk along the axis of rotation of the disk. The teeth are evenly spaced from each other throughout the circumference of the disk. The spaces between two adjacent teeth bound sockets wherein the impeller vanes are engaged by their respective shanks, enabling the vanes to be radially held through positive connection.
More precisely, in reference to FIG. 2, the shank 15 of the first vane 10 of FIG. 1 successively includes along the longitudinal axis X of the vane, from the blade 11: a pole 16, a neck 17 and a bulb 18, which have planar side flanks 19. The bulb extends along a longitudinal axis Y, substantially perpendicular to the longitudinal axis X of the vane. When the first vane 10 is in position on the disk, these side flanks 19 are aligned with the side faces of the disk. The neck 17 and the bulb 18 have a cross-section corresponding to that of a socket so as to radially hold the first vane 10. Indeed, as seen from the leading edge 12 side as illustrated in FIG. 3, the neck 17 is characterised by a narrow area and the bulb 18 by a flared area, so as to radially retain the shank 15 in the socket.
Further, the pole 16 includes side walls 20 extending on most of the pole 16 along the longitudinal axis X, in a plane substantially orthogonal to the longitudinal axis Y of the bulb 18. The walls enable swinging of the first vane 10 towards the disk from the active surface towards the passive surface or reversely to be prevented. Hereinafter, the dimension of the walls 10 along the axial direction Y will be called thickness E.
In order to reduce the weight of the turbine impeller, it is proposed to reduce the disk diameter as well as the thickness of the walls of the vanes throughout their height. A lower portion of a second vane 40 according to this new configuration is illustrated in FIG. 4. The second vane 40 includes a shank 41 comprising a pole 42, a neck 45 and a bulb 46, the pole 42 including walls 43. FIG. 4 gives details about the shank 41. It is noted that the height H of the pole 42 is increased with respect to the first vane 10 of FIG. 1 in order to compensate for the reduction in diameter of the disk, and that the walls 43 are of lower thickness. The walls 43 define a first area 44 on the active surface side of the second vane 40 and a second area on the passive surface side of the second vane 40.
However, these modifications cause two problems:                each tooth 60 of the disk 61 includes, at its top 62, that is in the area farthest from the axis of the disk 61, chamfers 61 located at the side faces 64 of the disk 61, as illustrated in FIG. 5. More precisely, each tooth 60 includes two chamfers 63 at each of the side faces 64 of the disk 61. Thereafter, in reference to FIG. 6, the dimension of the chamfer 63 along the leading edge/trailing edge direction will be called length L. But, since the walls 43 are of low thickness E, they can be supported on the teeth 60 only at the chamfer 63, that is be unstably supported. This situation occurs if the thickness E of the walls 43 is equal to or lower than the length L of the chamfers 63. A swing of the second vane 40 can then happen, upon mounting the second vane 40 onto the disk 61 or in operation. A magnification of the area of the chamfer of FIG. 6 is given in FIG. 7.        The neck 45 has an overstress area, which decreases the robustness of the second vane 40.        